A spectrum of light is commonly represented by a chart illustrating a magnitude of light plotted as a function of wavelength. For example, a spectrum may exist for a light output device or light from a light output device after the light has been scattered from a substance.
Color is a physiological response to a spectrum of light. A color may arise from a response to a narrow band spectrum (e.g., monochromatic light) or a broader spectrum of light. For example, color may be a response to a spectrum of a light output device (if the light is directly incident on an eye) or a response to a spectrum that results after the light from the light output device is scattered from a substance (if the light is viewed after the light is incident on the substance).
Perception of a color in response to viewing a spectrum of light results from a brain's interpretation of outputs of an eye's three different types of cones in response to the spectrum. A color that is perceived in response to viewing a spectrum of light is commonly referred to as an apparent color. Since many different spectra can give rise to the same outputs from the cones, a given color can be percieved when any of the different spectra is incident on the eye.
Colors that appear the same but result from different spectra are referred to as metameric colors, or simply metamers.